Integrated water treatment control system with probe failure detection

ABSTRACT

The integrated water treatment control system incorporates control of filtration, heating, chemical treatment and water conditioning; a programmable display shows values of key parameters, operational settings and system status; a user-selectable multi-line, multi-language display panel has menus and submenus; a remote access displays through modems and computers; an in-line computation of water saturation index handles sensor and panel keyboard inputs; and a dynamic probe failure detection system is also included.

BACKGROUND OF THE INVENTION

The invention relates to a water treatment control system, particularlyone that integrates the control of various aspects of a water reservoiror stream using various probes and which includes provision for probefailure detection. Modern water treatment requires the use of bothphysical and chemical processes. They have traditionally been controlledindependently. Typical applications of water treatment systems include,but are not limited to, municipal or industrial water treatment plants,cooling towers, swimming pools, agricultural or food processing plants,and carwash systems.

The physical processes include pumping of the water being treatedthrough filters to remove suspended particles and replacement ofcontaminated water with fresh water. The chemical processes includeinjection of sanitizers, oxidizers, pH adjustment chemicals, biocidesand other chemicals. In addition, heaters or coolers are used tomaintain proper water temperature.

All these processes depend on the use of sensors, timers and outputs forcontrol and monitoring, including remote display and operation. Becausethe equipment is usually made by different manufacturers, each processhas an independent control system which results in large, cumbersomeinstallations and a lack of compatibility and an inability tocommunicate between different instruments.

An object of the present invention is to integrate all the monitoringand control functions into a single control unit using a microprocessorto manage the different processes. Such an integrated control systemmakes it easy for the operator to supervise all the different aspects ofthe water treatment system and to respond rapidly to any malfunction orother emergency.

Another object is to access the control unit remotely by modem andcomputer, and simulate the display remotely of the actual on-site panelfor the purpose of monitoring and control from a remote location.

A further object of the invention, using a microprocessor, is themonitoring of water balance conditions through the computation of thesaturation index, or Langelier Index, based on water pH, temperature,alkalinity and hardness. This index shows whether the water is properlybalanced, or corrosive, or scaling.

Still another object, using a microprocessor, includes a dynamic probefailure test based on recovery analysis of an induced sensor offsetcondition. This test is more reliable and more general than static probefailure testing used in conventional applications. In particular, it canbe applied to any type of sensing element.

BRIEF SUMMARY OF THE INVENTION

The invention provides an integrated water treatment control system fora water source. The system includes various water treatment elements aswell as first means to circulate water from the water source through thewater treatment elements, and second means to sense multiple physicalcharacteristics of the circulated water and to determine if the sensedcharacteristics are within or outside a given range, and to produce afirst signal when the sensed characteristics are outside a given range.Third means are also provided to treat the circulating water in responseto the first signal until the characteristics sensed to be outside therange return to within the given range.

In particular, the present system provides a water treatment controlsystem in which the sensed characteristics may include clogging of afilter through which the circulating water stream passes, temperaturevariations of the circulating water stream within and outside the givenrange, the pH of the water stream, particulate inclusions within thewater stream, dissolved solids within the water stream, the oxidationreduction potential (ORP) of the water stream and the conductivity ofthe water stream. In response to any one or more of these sensedconditions being outside a given range, treatment of the water stream isaffected to return the sensed condition to within the given range.

Preferably the system employs probes to detect various of the sensedconditions, and also provides for periodic checking of the probes tomake sure that they have not failed. To detect failure of a probesensor, the system preferably includes a fifth means to accept andtemporarily store the output of the sensor, sixth means to temporarilydisconnect the first signal from the third means and to apply an out ofrange signal to the fifth means, and seventh means to measure therecovery of the fifth means from the out of range signal, thereby todetect, by a failure to remove, the failure of the given sensor orprobe. Upon detection of such failure, means are also provided togenerate a sensor failure alarm. Further, preferably the seventh meansalso measures the out of range signal itself and generates a sensorfailure alarm when the out of range signal is excessive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in connection with theaccompanying drawings in which:

FIG. 1 is a schematic diagram of an integrated water treatment controlsystem constructed in accordance with the present invention;

FIG. 2 presents various screen displays of the controller included inthe system; and

FIG. 3 is a schematic diagram of a preferred open probe detectioncircuit included in the system.

DETAILED DESCRIPTION

The General System

As previously stated, the present integrated water treatment controlsystem may be used to monitor and treat most any source of water, andthe water in a swimming pool, or the water employed in food processingplant or carwash system. Often this water is drawn from the source,evaluated, then recirculated back to the source. At times the water maybe drawn from a municipal or other water supply, evaluated, then usedand not recirculated--agricultural systems often do this. The presentsystem can be used to evaluate most any flowing stream of water, whetherrecirculated or not.

FIG. 1 shows a schematic of the integrated water treatment controlinstalled along the tubing of a flowing stream of water. The water ispumped through a circulation line 10 by pump 11. In line 10 is a filter12, heater 14, chemical injection points 16, bleed valve 20, and fillvalve 22. The pump may be Model 11-090 made by Sta-Rite Industrieslocated at 600 Jefferson St., Waterford, Wis. 53185. The filter may beModel 13-035 made by StaRite Industries located at 600 Jefferson St.,Waterford, Wis. 53185.

Sensors 23 are mounted either directly on the main circulation line 10or on a bypass line 24 for sampling of the water. The various sensors 23send their signals to a control unit 28 where they are processed fordisplay, analysis and activation of the different chemical feeders,heater, filter valves, as well as the bleed and fill valves.

Included in sensors 23 is a pH sensor 32. It monitors the acidity of thewater and is used to determine the activation of the chemical feedersfor acid or base feed. Such a sensor is sold by Cole-Parmer located inNiles, Ill., the sensor being designated as sensor model H-05994-30.

A PPM sensor 34 is used to monitor the concentration of sanitizer usingan amperometric or potentiostatic measurement. Such a sensor ismanufactured by Fisher-Rosemount located in Irvine, Calif., the sensorbeing designated as sensor model 499 TFC.

An ORP sensor 36 measures the oxidation-reduction potential of thesanitizer, which is related to its activity. Such a sensor is sold byCole-Parmer located in Niles, Ill., the sensor being designated assensor model H-27006-21. The input from either sensor 34 or 36 (or both)can be used to determine activation of a chemical feeder 42 formaintaining the proper sanitizer level in the flowing water stream. Asimilar feeder can also be used to reduce the concentration of excesssanitizer by adding a reducing agent, such as after superchlorination ofa swimming pool.

Temperature sensor 44 monitors the temperature of the flowing waterstream, and is used to regulate the thermostat of the heater 14 in awell known fashion. In addition, temperature data can be employed bycontrol unit 28 to correct the signals of other sensors such as pH, ORPand conductivity which are temperature dependent. Such a sensor ismanufactured by Cole-Parmer located in Niles, Ill., the sensor beingdesignated as sensor model H-93824-00. The heater 14 may, for example,be model 16-045 made by Teledyne Laars located in Moorpark, Calif.93021.

A conductivity sensor 46 monitors the conductivity of the water and isused to determine the Total Dissolved Solids (TDS) in the water and todetermine initiation of water replacement through the bleed and fillvalves 20 and 22. This is particularly applicable to cooling towers,swimming pools and hot water spas which are subject to evaporation andconcentration of dissolved solids. A presently preferred sensor ismanufactured by Signet Scientific Co. located in El Monte, Calif., thesensor being designated as sensor model 3-2820-1.

Additionally, a safety flow switch 48 can be installed on the bypassline 24 to alert the control unit to a lack of water flow and erroneousreadings if the bypass line is shut off or becomes obstructed. Such aswitch may be model RF2000P made by GEMS located in Plainville, Conn.

A flow rate sensor 52 is installed on the main recirculation line 10 tomonitor the flow of water in the recirculation line 24 and to enable thecontrol unit to keep track of the cumulative amount of water goingthrough the filter 12. A presently preferred sensor 52 is manufacturedby OMEGA located in Stamford, Conn., the sensor being designated assensor model FP-6000. Flow interruption results in an alarm conditionand shutdown of the chemical feeders 42. Cumulative flow rate may beintegrated by control unit 28 and used as an option to determineinitiation of backwashing of the filter.

Two pressure sensors 54 and 56, or a differential pressure unit, areinstalled before and after the filter to determine water pressure dropacross the filter. They are used to determine proper pump operation andinitiation of filter backwashing when it becomes overloaded with dirt,debris and impurities. A presently preferred pressure sensor is sold byOmega Engineering located in Stamford, Conn., the sensor beingdesignated as sensor model PX 242-060G5V.

The chemical feeders, collectively designated as 60, are used forinjection of chemicals from the various tanks for water treatment,including but not limited to sanitizers, pH control chemicals (acid orbase), oxidizers, inhibitors, biocides and algicides. Appropriatechemical feeders are those manufactured by Pulsafeeder located in PuntaGorda, Fla., and identified as model Dolphin-50.

Backwashing of the filter is done to clean the filter by applying a"backwash" signal 62 to the filter to reverse the flow of water throughthe sand or filter medium thereby to dislodge accumulated particles anddebris which reduce the flow of water. This is controlled by the programof the control unit to activate the proper valves for flow reversal,flushing water to waste and refilling as required. It can be initiatedautomatically by programming for elapsed time, or for pressuredifferential across The filter or accumulated water flow. It can also beprogrammed with a combination of these factors, such as time anddifferential pressure. In large installations with several filters,backwashing is done sequentially, one filter after another with a waittime between each filter to assure proper closure of the valves.

All data is displayed on a panel display 64 of control unit 28, and isavailable for remote monitoring and data logging over phone lines 66through modems or other devices connected to computer 68. The data canalso be stored in the control unit on memory files or chips.

The Controller

A prototype of the present system has been constructed. Whilepreliminary tests indicate that generally it performs in a satisfactoryfashion, further testing remains to be completed. In particular, controlunit 28 has been loaded with a computer program to process the varioussensor inputs for display analysis and activation of the differentelements to treat the circulating water through line 10. The presentlypreferred system employs as a central processing unit a S80C652-2A68manufactured by Phillips, operating at 16 MHZ. It also includes a PROMarray such as one using models 1-27C010 and 3-27C256 manufactured byNational Semiconductor. The PROM is connected to the CPU and stores thecomputer program for controlling the various operations and processes ofthe control system. A computer program which can be fully loaded intothe control unit has not been fully tested and debugged but is believedto operate in a reasonably satisfactory fashion at present to effect themajor processing, display, analysis and activation functions of thecontrol unit. Its integration into the controller and the activation bythe controller of the various elements of the system is believed to bereadily apparent and well within the skill of those of ordinaryabilities in the design and implementation of such control systems.

Programmable Display Menu

Because of the complexity of the system, it is highly desirable to use amicroprocessor-based controller or control unit 28 with a multi-line,multi-screen, multi-language, multi-unit display that allows the displayand correction of information for the different processes. This reduceshardware requirements such as display lights, readouts, switches, etc.

An example of an 8-line multi-screen display 64 is shown in FIG. 2. Thefirst three screens or screen areas 70, 72 and 74 are continuouslyscrolled to show the status of the different systems, the readings ofthe sensors and the control settings.

The last screen or screen area 76 is an example of a submenu, in thiscase the submenu for ORP, with the different options for thesub-submenus, such as Calibration of the sensor, Setpoint for control,Alarms high and low, Limit Timer for overfeed protection and actual RunTime. All the different parameters may offer similar submenus. Thisallows a high degree of flexibility in the programmable functionsavailable to the operator.

Remote Access by Computer

Remote computer access of the water treatment controller 28 is importantfor operators of multiple facilities, particularly if they are spreadover large geographic areas. The present invention allows actualoperation of the controller through modems and telephone lines or radiotransmission with a simulated display at remote computer 68 thatcorresponds to the actual display produced by the on-site control unit.

The remote unit operator can get real-time readings of the differentsensors and operating conditions. The operator can also change thesettings, subject to password security protection, and may accessseveral units at one location over one phone line, if desired.

On-Line Computation of Saturation Index

The saturation index (SI), also known as the Langelier Index, isemployed in the control unit 28 to determine whether the water in line10 is corrosive or is subject to scaling by precipitation of calciumcarbonate. This is particularly important in cooling tower and swimmingpool applications to extend the longevity of the equipment.

The Langelier Index is calculated through a formula of the type:

    SI=pH+TF+CF+AF-12.1

Properly balanced water requires an SI value near zero. If the SI valueis above 0.3, the water is scaling. If the SI value is below -0.3, thewater is corrosive to plaster and metallic parts.

In the Langelier Index formula, pH represents the acidity of the waterand is normally determined with the pH sensor 32, or electrode, that ispart of the control system. TF is a temperature factor that is alsodetermined by a temperature probe 44 that is part of the system. CF isthe Calcium Hardness factor which is not easily determined with asensor. In that case, the Calcium Hardness can be determined with a testkit and the resulting value manually entered through the panel keyboard80 on the control unit. AF is the Alkalinity Factor which is alsodetermined with a test kit and entered manually through keyboard entry.

Previously, calculation of SI required the use of special tables whichmany operators find difficult to manipulate. The system described hereautomatically calculates the Saturation Index and displays the resultingvalue and water condition on the display panel. If the water becomescorrosive or scaling, the operator is immediately alerted by an alarm onthe display screen 64.

The operator can also use the program to calculate what-if simulationsby manually entering values for pH and temperature that are normallyobtained from the sensors. Two of the parameters, Calcium Hardness andAlkalinity, are not obtained from sensor readings but rather from testkits and manual entries. This is not a serious problem since they areslow to change in value, whereas the other two, pH and temperature, canchange rapidly. It is sufficient for the operator to manually check andupdate these values periodically.

Dynamic Probe Failure Detection

Probe failure can cause serious problems in automatic control systemsthat are designed to run unattended for long periods of time. Forinstance, false sensor readings can result in overfeeding orunderfeeding of chemicals, both of which can have adverse effects on theequipment and/or users.

Conventional probe failure detection systems are of two kinds. Thesimplest and least effective system depends on the failure to cause anout-of-range alarm condition. The second and more effective systemdepends on monitoring a physical property of the sensor itself, such asits resistance or impedance, which is not always possible or reliable.Both of these systems are basically passive and static. Either approachat times may not detect failure of a probe.

The present invention preferably uses a dynamic probe failure detectionsystem, one in which the sensor signal is purposely changed from itsactual reading for a short period of time then released to recover. Thecontroller checks to see if the true value is restored within areasonable amount of time. Even though this system requires moresophisticated electronics, it offers much better protection for thesystem and processed water. Another advantage is that it can be appliedto any type of sensing device. Additional advantages include:

A. It is transparent to probe application device; i.e., has no effect onthe probe input signal to the measuring and/or controlling system.

B. It can be made to work on either polarity probe.

C. It can be made to work with small or large signals.

D. It detects either a shorted probe (pinched wire, corrosion) or openprobe (broken probe, cut wire, disconnected plug).

E. It will work with "static" (infinite load resistance) voltage probes.

A preferred dynamic probe failure detection system is schematicallyillustrated in FIG. 3. It includes various elements or components thatoperate and interrelate in a periodic manner. Specifically, every minutefor example as set by the "Test Frequency Generator" 102, the probeinput 104 is disconnected, by "Reed Relay 1" 106, from the applicationdevice (e.g. the controller 28) for a few seconds (10 seconds forexample), as preset by the "Test Interval" unit 108. During this testinterval the application device is supplied with the same signal it hadbefore the test interval using a film capacitor analog memory includedin the "Probe Voltage Buffer Amp With Memory" 110. This prevents anyupset in the application.

At the beginning of the test, the probe voltage in probe voltage buffer112 is forced for a few milliseconds (20 mS for example), as preset bythe "Logic," to a voltage about 50 mV higher, for example, than it hadbefore the test interval. This voltage is generated by the "Force ProbeCircuit" 120. Reed relay "2" 122 connects the probe to this forcingvoltage source. After the probe is released from the forcing voltage,the buffer amp 112 should recover to its previous value before the endof the test interval. A comparator circuit, "Probe Recovered Circuit"126, verifies that the probe voltage, from the "Probe Voltage BufferAmp" (without memory) did recover to near (within 25 mV for example) itsprevious value. If it does not recover, a signal is applied to "Logic"circuit 130 over line 131. Another part of the "Force Probe Circuit" 120checks the current needed to force the probe voltage. If it is more thana few microamps (50 uA for example), an "Excess Current" condition issent to the "Logic" circuit 130 over line 132.

If, at the end of the test interval, either the probe fails to recoveror excess forcing current was detected, the "probe fail" output isactivated by the "Logic" circuit 130 over line 134, which signal itapplied to controller 28.

In general, concerning the system preferably all components are proven,readily available and off the shelf. Power supply voltages areappropriate to the components used. Reed relays are preferred becausethey have the greatest "off" state resistance. Buffer amplifiers such asamplifier 110 preferably have MOS inputs because neither the probe northe memory capacitor may have the ability to generate or retainappreciable current. Preferably the probe signal is fairly large so thatbuffer amplifiers may have a relatively modest DC gain, such as a gainof 3. However, a gain range (depending on the probe voltage andapplication device needs) anywhere from 0.05 to 200 can be used ifdesired. Probe voltages typically are DC and in the range of +400 to+900 mV. But the present circuit system can employ smaller, larger,negative or bipolar voltage values if desired. The logic circuit 130includes a power on reset delay to assure that normal probe operationhas time to stabilize before any test interval is initiated after thesystem is turned on or reset.

The overall concept of the circuit is to temporarily store the presentprobe voltage (whether amplified or not), force the probe to a slightlydifferent voltage (measuring current while doing so to see if there is ashorted line or probe), and let the probe return to its normal operatingvalue if it can (not defective probe or an open line). The times allowedfor the test to occur preferably are based on observing the particularprobe's output in response to a forced voltage change.

Another consideration in the present circuit design is to pick a forcingtest voltage to be such that the application device (e.g. chemical pump)would eventually turn off if an open probe occurred. For example, if theprobe sensed the chlorine level in the water stream, and triggered apump to add chlorine when a low level had been detected, the forcingtest voltage and its associated circuitry would be of a polarity andlevel that would tend to turn the pump off if an open probe conditionoccurred. This may be accomplished by applying the forcing test voltageto a capacitor that is discharged by a good probe, but retains andaccumulates the applied charge with each forcing test voltage cycle ifan open probe condition has occurred. This accumulated voltage isapplied to controller 28 to shut off the output in the event of a badprobe determination.

While the presently preferred system has been illustrated and described,variations in the system and in its elements and design may be preferredby others of ordinary skill in the design and implementation of suchcontrol systems. Accordingly, the invention is not limited to thepreferred embodiment, but rather is as set forth in the followingclaims.

What is claimed is:
 1. An integrated water treatment control system fora water source, the system including:water treatment elements; firstmeans to circulate water through the water treatment elements; a secondmeans to sense multiple physical characteristics of the circulatingwater including a means to sense temperature and to adjust the sensedmultiple physical characteristics in response to sensed temperature andto determine if the adjusted sensed characteristics are within oroutside a given range, and to produce a first signal when any one ormore of the adjusted sensed characteristics are outside the given range;third means to treat the circulating water in response to the firstsignal until the adjusted characteristics sensed to be outside the rangereturn to within the range; and fourth means connected to the secondmeans to detect the failure of a sensor, the fourth means including:fifth means to accept and temporarily store the output of the sensor,sixth means to temporarily disconnect the first signal from the thirdmeans and to temporarily apply a forcing voltage to the sensor, andseventh means to measure the recovery of the output of the sensor afterremoval of the forcing voltage, thereby to detect failure of the sensorand, upon detection of said failure, to generate a sensor failure alarmsignal.
 2. An integrated water treatment control system as set forth inclaim 1 in which at least one of the water treatment elements includes afilter, and in which the second means senses clogging of the filter, andin which the third means treats the filter by causing a backwashcondition through the filter for an interval sufficient to substantiallyunclog the filter.
 3. An integrated water treatment control system asset forth in claim 2 in which the water treatment elements include atotal dissolved solids element, and in which the second means senses theconductivity of the circulating water to determine the total dissolvedsolids in the water, and in which the third means treats circulatingwater to return the total dissolved solids to with a given range;thewater treatment elements include a heater, and in which the second meanssenses the temperature of the circulating water, and in which the thirdmeans treats the circulating water in a manner to return the temperatureof the recirculating water to within a given range, the water treatmentelements include a pH adjusting components, and in which the secondmeans senses the pH of the circulating water, and in which the thirdmeans treats the circulating water in a manner to adjust acidity oralkalinity to a pH within a given range; the water treatment elementsincludes a sanitizer, and in which the second means includes a sensor tomeasure the oxidation-reduction potential of the circulating water, andin which the third means treats the circulating water to return the ORPlevel to within a given range, and in which the second means includes aPPM sensor to sense the concentration of sanitizer in the circulatingwater and in which the third means treats the circulating water tomaintain the concentration of sanitizer within a given range.
 4. Anintegrated water treatment control system as set forth in claim 3 inwhich the seventh means also measures applications of current needed toapply the forcing voltage to the sensor and generates a sensor failurealarm signal when an amount of current needed is excessive.
 5. Anintegrated water treatment control system as set forth in claim 2, inwhich the second means senses and integrates the volume flowing throughthe filter, and produces a signal representative of the integrated flow.6. An integrated water treatment control system as set forth in claim 5,in which the second means further includes a timing means to sense theperiod of time since the last backwash and produces a signalrepresentative of that period of time and further includes adifferential pressure means which senses the pressure drop across thefilter and produces a signal representative of the pressure drop.
 7. Anintegrated water treatment control system as set forth in claim 5 inwhich each of the signals produced by the second means is monitored andif any one of the signals is outside of a given range, a backwashtreatment of the filter is initiated.
 8. An integrated water controlsystem as set forth in claim 2 which further includes means fordetermining and displaying the Saturation Index.
 9. An integrated watercontrol system as set forth in claim 8, which further includes an alarmsignal which is generated if the Saturation Index is outside of a givenrange.
 10. An integrated water treatment control system as set forth inclaim 1 in which the seventh means also measures applications of currentneeded to apply the forcing voltage to the sensor and generates a sensorfailure alarm signal when an amount of current needed is excessive. 11.An integrated water treatment control system for a water source, thesystem including:water treatment elements; first means to circulatewater through the water treatment elements; a second means to sensemultiple physical characteristics of the circulating water including ameans to sense temperature and to adjust the sensed multiple physicalcharacteristics in response to sensed temperature and to determine ifthe adjusted sensed characteristics are within or outside a given range,and to produce a first signal when any one or more of the adjustedsensed characteristics are outside the given range; a local display andcontrol means located at the site of the water treatment elements whichdisplays adjusted sensed characteristics and provides means for alteringa plurality of operational parameters; third means to treat thecirculating water in response to the first signal until the adjustedcharacteristics sensed to be outside the range return to within therange; and fourth means connected to the second means to detect thefailure of a sensor, the fourth means including: fifth means to acceptand temporarily store the output of the sensor, sixth means totemporarily disconnect the first signal from the third means and totemporarily apply a forcing voltage to the sensor, and seventh means tomeasure the recovery of the output of the sensor after removal of theforcing voltage, thereby to detect failure of the sensor and, upondetection of said failure, to generate a sensor failure alarm signal; aremote display and control means which displays adjusted sensedcharacteristics and provides means for altering a plurality ofoperational parameters in substantially the same manner as the localdisplay and control means whereby an operator can control at a centralstation a plurality of remotely located integrated water control systemsby interacting with the remote display and control means insubstantially the same manner as at the local display and controlsystem.
 12. An integrated water treatment control system as set forth inclaim 11 in which the seventh means also measures applications ofcurrent needed to apply the forcing voltage to the sensor and generatesa sensor failure alarm signal when an amount of current needed isexcessive.